The invention relates to a device for handling thin sections, in particular cryosections. The invention is further concerned with a process for freeze-drying sections of this nature.
In order to examine, in the electron microscope, organic preparations in the form of thin sections (cryosections) which are kept at low temperatures and are obtained by means of ultramicrotomes, it is necessary to subject the cryosections to a preliminary treatment which is designed to render them suitable for examination. This preliminary treatment calls for a pressing operation, followed by a freeze-drying operation and cautious warming to room temperature. For this purpose, the cryosections must firstly be transferred from the cold chamber of the ultramicrotome into a pressing appliance from which they are then brought, in turn, into a freeze-drying chamber. After the freeze-drying operation and warming to room temperature, they are then picked up and secured in the electron microscope by means of a holder. Small carrier grids are used for transporting the cryosections, these grids being made of carbon or beryllium. The cryosections, removed directly from the knife of the ultramicrotome, for example, by means of a hair, are transferred onto these carrier grids which must, due to their small size, be handled by means of tweezer-like tools. The operation of pressing the cryosections against the carrier grids is carried out with the aid of weights which possess polished surfaces.
When employing this known procedure, it is impossible, during the various operations, to prevent cryosections from being lost, becoming unusable, or, at least, being adversely affected to such an extent as to be of only limited suitability for examination by electron microscopy. First of all, during the operation of removing the carrier grid, and the cryosection present thereon, from the cold chamber of the microtome, there is a danger of the cryosection falling from the carrier grid as a result of the draught of air accompanying this operation. Furthermore, due to its very low mass, the carrier grid heats up very rapidly in the course of its short journey to the pressing tool, as a result of which the cryosection is also warmed prematurely, and is thereby adversely affected. During the operation of mounting the carrier grids in the pressing appliance and, also, later, in the receiving fixture of an electron microscope - following freeze-drying and warming - there is always the danger that contaminants will reach the preparation as a result of handling. Moreover, the pressing tools must be kept most scrupulously clean, in order to prevent the cryosections from being contaminated and, as a result, becoming unusable. Finally, during the course of the drying operation, it is almost impossible to prevent the cryosections from losing their initially flattened shape and becoming domed.
These disadvantages lead to the situation in which, despite the existence of very good, easily-operated ultramicrotomes, the preparation of cryosections for examination by electron microscopy has not yet become a routine operation, but is a matter for highly-specialized personnel, and even such specialists are not spared a comparatively high spoilage rate.